The present invention relates generally to battery monitoring systems such as battery modules used with uninterruptible power supply (UPS) systems.
To provide continuous power to a load in applications that require continuity of power, such as in hospitals and critical processes in both industrial and commercial settings, a UPS system is typically used to switch between a primary and one or more alternate power sources in the event of failure or instability of the primary source. FIG. 1 illustrates portions of a typical UPS system 10. One or more input power lines are connected to a UPS module 12, and a battery module 14 is connected to the UPS module. If the input power fails, the battery module 14 provides power to the UPS module 12. The battery back up power may be required when power from the AC power sources are performing outside of acceptable limits or fail completely.
Battery monitoring systems are often employed to monitor the battery modules and insure that viable back-up power exists. With some known battery monitoring systems, a wire is run from each battery measuring point to a single central voltage data collection point. For series strings of batteries, such a wiring arrangement can be problematic for a variety of reasons. For instance, high voltages are involved and there are potential safety agency issues. Small wires are difficult to protect and install in a heavy current environment, and the wiring may be vulnerable, and particularly prone to damage during field battery maintenance. Isolation is required at the collection point, making accurate differential measurements difficult.
Further, the wiring can be expensive, and factory installation typically exhibits high labor costs. Because of the wiring, after-market field installation costs can cost as much or more than the monitoring equipment itself. Prior to installation, wired battery monitor systems require a site survey. Multiple custom battery rack configurations make determining wiring needs difficult. Wired battery monitor systems require up-front knowledge of the battery room configuration to determine wire lengths, conduit runs, etc. Inaccurate site surveys can cause significant back charges for revisions.
Additionally, long strings of batteries will become charge-imbalanced over time, thus affecting reliability and autonomous battery operation time. Imbalanced battery strings also will exhibit a lessened life expectancy for some of the individual batteries.
The present application addresses shortcomings associated with the prior art.